Okay, so after a day or so of use, I've determined the following with the headphones that I have.
The JVC SZ-1000, driven well, needs the bass boost. Then you get the headshake these headphones are known for. They are a little congested, due to muted highs, but the bass is all there for a bass head like me.
Logitech UE6000. Don't need to turn on the ANC/amp with this player. Sound is rich and full. Turning on ANC/amp introduces hiss and some artifacts. Not my favorite with the player.
Beats by Dre Tour V2 IEM's. Bass is VERY present. Overpowering really. Turning down the EQ settings is good, but not my favorite with these. They sound too congested with the player. With the iPod, they rocked, and I was thoroughly impressed with them, thinking Beats did a real trick with these, making them better than the originals. But they don't mesh well with this player.
Atrio MG7's. These have to be my favorite headphone with this player period. I've been considering a new set of IEM's, and I was listening to the Lord of the Rings: The Fellowship of the Rings soundtrack with these and the player with 44.1/16 FLAC files. I was thinking, I have to find something that sounds as good as these. Then I thought, why bother, these sound GREAT! By far my favorites.
Overall, the player is great, I haven't had any hiccups with it, and I've tried the gapless playback with the file search function, and it works just fine, playing back my "Celebration Day" FLAC's from Led Zeppelin. Smooth transition from file to file, without clicks or pops, just next track.
Loving this little player, and can't wait to get my 128Gb card, to put all my music on it. Having my entire library in CD quality, is just a fantastic prospect.